We are on vacation and after leaving the mooring from an overnight stay noticed that the batteries were not charging while running the engine at near cruising speed. All connections appear tight. The alternator output voltage is the same as the batteries and the charge light does not go out. Is their a way that we can test the alternator or troubleshoot this problem. No service is available on weekends in Maine. Hunter 410, 2002, Yanmar 4JH3E with 115 Amp Hitachi alternator.
Alternator Troubleshooting
- Thread starter Mahina Kai
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troubleshooting
You say that the Alternator is putting out the same voltage as the Batteries, this is a flag. Alternators should put out about 2 to 3 volts more than the batteries. Check the Alternator with no load( batteries), you should see about 14 volts with a Volt meter also be sure that a cell in the batteries has not gone dry. The description you gave sounds like that a diode in the alternator has gone out. fair winds AL
You say that the Alternator is putting out the same voltage as the Batteries, this is a flag. Alternators should put out about 2 to 3 volts more than the batteries. Check the Alternator with no load( batteries), you should see about 14 volts with a Volt meter also be sure that a cell in the batteries has not gone dry. The description you gave sounds like that a diode in the alternator has gone out. fair winds AL
Oops, be careful.....
If I read Al's advice, he is sugesting that you disconnect the batteries after the engine is running and measure the output of the alternator and the battery voltage for comparison. Many disconnect switches do not open the field connection to the alternator and without this disconnect feature the alternator output voltage will rise to voltages that may cause damage to itself. Don't do this, there is an alternate method. Before starting the engine, measure the batteries (house and/or starting) and write down the values. Then start the engine, bump the rpm up to about 1500 and measure the battery voltages again. Without the engine running, the normal battery voltage for the starting battery should be about 12.6 - 12.7. This may vary somewhat lower if the battery has not been charged by the alternator recently. If the alternator is charging, the voltage with the engine running should be over 13.2 and may be as high as 14.4 depending upon the battery's state of charge (or discharge). A higher voltage than 14.4 could indicate that there is a bad connection to the batteries and not allowing charging current to flow. If you find that the voltage with the engine running is less than 13.2 volts, you can be reasonably sure that you do have a charging problem. The voltage at the alternator and at the batteries should be within 0.1-0.2 volts of each other. A greater difference would indicate a bad connection between the alternator and the batteries. The fault could be one or more of the rectifing diodes or a fault in the diode-trio that feeds the alternator field winding internally. Either of these faults should be able to be repaired by a competent shop or by yourself if you are knowledgeable. It could also be the internal regulator, but that is a less common problem. Another fault that is easy to find and correct is a loose belt. The test for a loose belt is to FIRST STOP THE ENGINE. Then attempt to turn the fan/pulley on the alternator with your hand. If the belt is tight you will not be able to turn the pulley and cause the belt to slip. If you can turn the fan/pulley, then the belt is too loose. Simply tighten it and repeat the test until you cannot move the fan/pulley by hand. A loose or slipping belt will cause the charging fault light to come on and will not charge the batteries adequately. I hope this helps and that your vacation cruise is not hampered.
If I read Al's advice, he is sugesting that you disconnect the batteries after the engine is running and measure the output of the alternator and the battery voltage for comparison. Many disconnect switches do not open the field connection to the alternator and without this disconnect feature the alternator output voltage will rise to voltages that may cause damage to itself. Don't do this, there is an alternate method. Before starting the engine, measure the batteries (house and/or starting) and write down the values. Then start the engine, bump the rpm up to about 1500 and measure the battery voltages again. Without the engine running, the normal battery voltage for the starting battery should be about 12.6 - 12.7. This may vary somewhat lower if the battery has not been charged by the alternator recently. If the alternator is charging, the voltage with the engine running should be over 13.2 and may be as high as 14.4 depending upon the battery's state of charge (or discharge). A higher voltage than 14.4 could indicate that there is a bad connection to the batteries and not allowing charging current to flow. If you find that the voltage with the engine running is less than 13.2 volts, you can be reasonably sure that you do have a charging problem. The voltage at the alternator and at the batteries should be within 0.1-0.2 volts of each other. A greater difference would indicate a bad connection between the alternator and the batteries. The fault could be one or more of the rectifing diodes or a fault in the diode-trio that feeds the alternator field winding internally. Either of these faults should be able to be repaired by a competent shop or by yourself if you are knowledgeable. It could also be the internal regulator, but that is a less common problem. Another fault that is easy to find and correct is a loose belt. The test for a loose belt is to FIRST STOP THE ENGINE. Then attempt to turn the fan/pulley on the alternator with your hand. If the belt is tight you will not be able to turn the pulley and cause the belt to slip. If you can turn the fan/pulley, then the belt is too loose. Simply tighten it and repeat the test until you cannot move the fan/pulley by hand. A loose or slipping belt will cause the charging fault light to come on and will not charge the batteries adequately. I hope this helps and that your vacation cruise is not hampered.
Alternator won't charge full batteries
Rich has good advice (check the belt!). However, if the batteries are fully charged and there are little or no loads then the alternator will not charge. Static Battery voltage without a charge source will be around 12.6-12.8. With the engine running the voltage at the battery should read 13.8- 14.4 volts. I believe every boat should have a copy of Nigel Calders Boatowners Mechanical and Electrical Manual which has complete electrical troubleshooting guides.
Rich has good advice (check the belt!). However, if the batteries are fully charged and there are little or no loads then the alternator will not charge. Static Battery voltage without a charge source will be around 12.6-12.8. With the engine running the voltage at the battery should read 13.8- 14.4 volts. I believe every boat should have a copy of Nigel Calders Boatowners Mechanical and Electrical Manual which has complete electrical troubleshooting guides.
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